City Theatrical Donuts S4 10°, SL 10°

Donuts are used in the color frame slot of an ellipsoidal reflector spotlight to sharpen gobo projections. Similar to the way the human eye sharpens focus when it squints, a donut reduces the aperture and sharpens the output of the fixture. There is some reduction in brightness to achieve this increase in sharpness but this is often a tradeoff that designers are willing to make.